This invention relates to differential transmission drives and, more particularly, it concerns a differential drive unit construction by which power supplied at a single driving shaft is transmitted to each of an aligned pair of driven or output shafts at independent and continuously variable speed ratios.
In U.S. Pat. No. 4,152,946, issued May 8, 1979, in the name of the present inventor, several embodiments of continuously variable transmissions (CVT) are disclosed in which three frame supported working bodies operate to transmit a mechanical power input to a rotatable output at continuously variable speed ratios within the design range of the transmission. For purposes of definition in this background discussion as well as in the ensuing detailed description of the present invention and in the appended claims, the three working bodies may be termed, respectively, an "alpha body" which is supported by the transmission frame to be concentric with a first axis, a "beta body" which is concentric with a second axis inclined with respect to and intersecting the first axis at a point of axes intersection, and an "omega body" carried by or forming part of the frame to be concentric also with the first axis. Although any one of these three bodies may be rotatable on the respective axes with which they are concentric, one of the three is held against rotation to provide a reaction torque whereas the other two bodies are rotatable and coupled either directly or by gearing to the respective input and output shafting of the transmission.
It is to be noted that the terms "alpha body," "beta body" and "omega body" are completely arbitrary and as such, do not restrict the components designated thereby either to the class of transmission represented by the disclosure of the aforementioned patent or to specific structure to be described hereinafter. The terms will, however, lend consistency of definition in the description to follow and facilitate an understanding of various speed relationships to be expressed by algebraic equations.
The infinitely or continuously variable speed ratio capability of such transmissions is achieved by providing one of the beta and omega bodies with a pair of rolling or traction surfaces which are surfaces of revolution about the concentric body axis and which are of variable radii along that axis in symmetry with the point of first and second axes intersection. Physically, such rolling surfaces will thus provide the one body with a biconical-like configuration. The other of the beta and omega bodies is provided with a pair of rolling or traction surfaces which are also surfaces of revolution about the concentric body axis but which are of relatively constant radius. The pairs of rolling surfaces on the beta and omega bodies are retained in frictional engagement with each other at two contact points or zones capable of positional adjustment to vary the ratio of the beta body surface radius (R.sub.b) to the omega body surface radius (R.sub.w). Thus, if the alpha body is rotatable at a velocity (.alpha.) about the first axis, the rotational speed of the beta body about the second axis in a fixed frame of reference is (.beta.) and the rotational speed of the omega body on the first axis is (.omega.), then the respective speeds of the three bodies are related by the following equation: EQU .omega.-.alpha.+(.alpha.-.beta.)R.sub.b /R.sub.w =0 (1)
Because one of either the beta or the alpha bodies extends within the other of such bodies, the radius ratio R.sub.b /R.sub.w may represent a value of either less than 1 (where R.sub.b is always less than R.sub.w) or more than 1 (where R.sub.b is always greater than R.sub.w). The function .rho. will be used hereinafter to designate either R.sub.b /R.sub.w or the reciprocal R.sub.w /R.sub.b, whichever is greater than 1, it being understood that .rho. or its reciprocal 1/.rho. are used appropriately.
A generally preferred mode of operating such transmissions has been to apply an input torque to the alpha body to carry the beta body in nutation and hold the omega body against rotation (.omega.=0). The beta body is linked with an output shaft rotatable on the first axis by gearing having a ratio factor (k) which theoretically may be of any value and also may be made either positive or negative depending on the particular gearing arrangement used. In light of the foregoing, where .theta. is unit output speed and taking into account the gearing ratio (k), the output/input speed ratio of the unit is determined by an equation: EQU .theta./.alpha.=1-k.rho.. (2)
A principal advantage of operating in the mode represented by equation (2) is that the physical parameters of such transmissions readily accommodate a range of values for the function (k.rho.) which permit a continuously variable output/input speed ratio range of from zero to 1 (1.0&gt;k.rho.&gt;0.5). Also, this range may be shifted to include an output reversal through zero merely by selecting a gear ratio (k) so that the function (k.rho.) brackets a numerical value of 1 (e.g. 1.2&gt;k.rho.&gt;0.7).
In addition to the aforementioned patent, reference is also made to U.S. Pat. No. Re. 29,328, reissued Aug. 2, 1977 in the name of Yves Jean Kemper; U.S. Pat. No. 4,112,779 and U.S. Pat. No. 4,112,780, the latter both having issued on Sept. 12, 1978, in the name of Yves Jean Kemper and Lucien Bigot. These issued patents disclose additional variations of the continuously variable transmission type referred to above. As will be seen from these several prior patents, the particular configuration of any one of the alpha, beta and omega bodies as defined herein may vary in the respectively disclosed embodiments.